Hitherto, as a technology for identifying an area of a subject in an image, a technology called visual attention is known (see, for example, NPLs 1 and 2).
In visual attention, luminance information, color information, and edge information are extracted from an input image that is input. On the basis of those extracted information items, an information map indicating the likelihood of an area being the subject in each area of the input image is created for each item of the extracted information.
Then, information obtained as a result of a filtering process using a DOG filter, or obtained in such a manner that the respective information maps are normalized by linear normalization and are added up, and thereafter are further normalized, is formed as a subject map. This subject map is information indicating the likelihood of the area being the subject in each area of the input image. Use of a subject map makes it possible to identify which area of the input image the subject is contained.
Here, as luminance information, an average value of R (red), G (green), and B (blue) components of the pixels of an input image is extracted from the input image, and as color information, a difference of the R and G components of the pixels of the input image, and a difference of the B and Y (yellow) components are extracted. Furthermore, edge strengths of each of the directions of 0 degrees, 45 degrees, 90 degrees, and 135 degrees are extracted from the input image by using a Gabor filter.